There are a lot of people looking at fuel efficiency as well as carbon/sox/nox emmissions. For the companies running ships, the more efficient the plant is, the

There are a lot of people looking at fuel efficiency as well as carbon/sox/nox emmissions. For the companies running ships, the more efficient the plant is, the more money they save on fuel. About ten years ago we did a rough back of the envelope calculation in one of my engineering classes when I asked a similar question. The extra weight of the solar panels would negate any small benefit they would provide plus the cost of maintaining extra equipment. A lot modern ships run a shaft generator which uses the power from the shaft turning the propellor to turn an alternator to make electricity. When the ship slows down at the end of the trip, they go back to running smaller 'port' generators.